Specification section
1.3
What do you need to learn?
The advantages and disadvantages of the following
thermoplastics when manufacturing products:
Acrylic, Polyethene, Polyvinyl Chloride, High Impact Polystyrene
and Acrylonitrile-Butadiene-Styrene (ABS).
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The advantages and disadvantages of the following
thermosetting plastics when manufacturing products:
Polyester Resin and Urea Formaldehyde.
Understand and describe the following properties when
selecting and using polymers in product manufacture:
Plasticity and Durability
Polymers 1.3
What is a Thermoplastic?
Thermoplastics can be re-heated and therefore
shaped in various ways.
They become mouldable after reheating as they do not
undergo significant chemical change.
Reheating and shaping can be repeated. The bond
between the molecules is weak and become weaker when
reheated, allowing reshaping.
Thermoplastics tend to be composed of 'long chain
monomers'. These types of plastics can be recycled.
These plastics possess a common property, they soften
when heated and are often used in schools to vacuum form
shapes.
Polymers 1.3
Acrylic (Known also as PERSPEX)
This is the most common plastic in a school workshop.
It is purchased usually in the form of sheets and comes
in a range of colours. It can be transparent, translucent
or opaque. It is resistant to most acids and weather
conditions.
Transparent – It is clear and light can pass through, think of a window.
Translucent - An object that allows light to pass through but is not
transparent, think tracing paper.
Opaque –
Light cannot go through the object.
Advantages
Fairly cheap, stiff, hard, durable,
good electrical insulator,
machines and polishes well
Disadvantages
Scratches easily and brittle
Uses
Signs, covers of storage boxes,
aircraft canopies and windows,
covers for car lights, wash
basins and baths
Polymers 1.3
Polyethene
Can be moulded into almost any form due to its
excellent moulding qualities.
It is available in large sheets and used for the
production of a variety of products because of its two
different densities:
High density: Which is rigid, hard, can be sterilised
and is resistant to corrosion.
Example of products made: Buckets, Bowls, Milk crates
Low density: Which is tough, soft, flexible, available in
a variety of colours and a good electrical insulator.
Example of products made: Squeezy bottles for
shampoo and washing up liquid, Toys, Carrier Bags
Advantages
LD - Tough, lightweight, durable, good
resistance to chemicals, flexible, fairly
soft, good electrical insulator
HD - Hard, stiff and able to be
sterilised
Disadvantages
Harmful to the environment –
Animals, water ways and some are
not recyclable
Uses
Packaging, especially bottles, toys,
packaging film and bags.
'Plastic' bottles, tubing, household
equipment
Polymers 1.3
Polyvinyl Chloride (PVC)
It is a tough material which can be purchased as a hard
material or alternatively a flexible form.
It can be welded or bonded with an adhesive. It has a
range of uses including water pipes, raincoats, records,
coating on electrical wires and many more.
Advantages
Stiff, hard, tough,
lightweight, good chemical
resistance
Disadvantages
Poor weatherability and
easily scratched
Uses
Pipes, guttering, bottles,
window frames
Polymers 1.3
Polystyrene
Polystyrene is one of those polymers that's all over the place.
Polystyrene is an inexpensive and hard plastic.
The outside housing of a computer is made of
polystyrene, as well as the housings of things
like hairdryers, TVs and kitchen appliances.
Model cars and airplanes are made from
polystyrene, as well as disposable razors and CD cases.
There's also foam packaging and insulation, and a lot of the moulded parts
on the inside of a car, like the radio knobs.
Advantages
Disadvantages
Light, hard, stiff,
Brittle, low impact
transparent, with good water polystyrene breaks very
resistance
easily, not strong
Uses
Toys, especially model kits,
packaging, castes for
televisions, 'plastic' boxes
and containers
Polymers 1.3
Acrylonitrile-Butadiene-Styrene (ABS)
ABS has many characteristics and is used for casings
for kitchen equipment (e.g. food processors), toys,
telephones, car components and tool handles to name
a few.
It is strong, tough, hard wearing,
light weight, durable and has a
good surface finish.
Advantages
Disadvantages
Strong, tough, hard, light,
Not weather resistant and
durable, good surface finish, opacity (opaque)
resists chemicals
Uses
Casings for kitchen
equipment (e.g. food
processors), toys,
telephones, car
components, tool handles
Polymers 1.3
What does Durability mean?
If a material withstands wear and tear, weather and corrosion
then the product is durable (long lasting). It usually is noticed
by a change in appearance when it starts to wear out.
Corrosion is the main area affecting durability and can often
be overlooked which can have serious effects on structures
such as bridges whose durability can be affected by rust.
Ultra violet light can affect materials, particularly plastics
which can become very brittle with the effects of the sun.
In general though, plastics are less likely to corrode than most
materials but strength is not usually associated with plastics.
Polymers 1.3
What is a Thermosetting plastic?
Once ‘set’ these plastics cannot be reheated to
soften, shape and mould.
The molecules of these plastics are cross linked in three
dimensions which result in a rigid molecular structure.
Thermosetting plastics will soften when heated for the first
time. This allows them to be shaped, but because they are
set in a rigid and permanently stiff molecular structure, they
cannot be reheated and reshaped like thermoplastics.
The bond between the molecules is very strong and
therefore cannot be recycled.
Polymers 1.3
Many adhesives (glues) are thermosetting plastics. A good example is
‘Araldite’ which is an epoxy resin that hardens when a second chemical is
added (a catalyst). It will bond most materials including woods and
metals as well as some plastics.
Polyester Resin
If resins are combined with a material such as fibre
glass the result is a very tough material that can resist
impact. This type of material is known as a glass
reinforced plastic (GRP) and is used in car body
repairs, sailing boats, corrugated sheet because of its
lightness, toughness and resistance to water.
Advantages
Stiff, hard, good electrical
insulator and cost effective
Disadvantages
Brittle unless laminated,
short shelf life, emissions
are harmful
Uses
Casting and encapsulation,
bonding of other materials
• Polymers 1.3
Urea Formaldehyde (UF)
Urea Formaldehyde has physical properties of
high hardness and high toughness, making it
suitable for strong, knock-resistant electrical
fittings.
It is also scratch resistant and a very good
electrical insulator, making electrical fittings
manufactured from this polymer safe to use.
Advantages
Stiff, hard, strong and a
good electrical insulator
Disadvantages
Brittle
Uses
Electrical fittings, handles
and control knobs
Polymers 1.3
What does Plasticity mean?
Plasticity means the ability of a
material to be changed in shape
permanently.
This diagram shows the ‘plasticity’
of molten aluminium by pouring it
into a mould. Once the aluminium
has cooled down, it can be
removed from the casting sand. It
has a new shape.